US20060206881A1 - Process scheduler employing adaptive partitioning of critical process threads - Google Patents

Abstract

A system is set forth that includes a processor, one or more memory storage units, and software code stored in the one or more memory storage units. The software code is executable by the processor to generate a plurality of adaptive partitions that are each associated with one or more process threads. Each of the plurality of adaptive partitions has a corresponding processor time budget. One or more of the process threads are designated as critical threads. Each adaptive partition associated with a critical thread is assigned a corresponding critical time budget. The software code also includes a scheduling system that is executable by the processor for selectively allocating the processor to run the process threads based, at least in part, on the processor time budgets of the respective adaptive partitions. The scheduling system may allocate the processor to run a critical thread based on the available critical time budget of the associated adaptive partition even when the processor time budget of the associated adaptive partition has been exhausted. In one example, the scheduling system functions SO that it only bills the critical time budget of an adaptive partition for time used to run an associated critical thread when the processor is overloaded and the critical time budget for the adaptive partition is concurrently exhausted. Methods of implementing such a system are also set forth.

Description

PRIORITY CLAIM
• This application claims the benefit of priority from U.S. Provisional Application No. 60/662,070, filed Mar. 14, 2005, which is incorporated herein by reference. This application is also a divisional of U.S. patent application Ser. No. 11/317,468, filed Dec. 22, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/216,795, filed Aug. 31, 2005, both of which are also incorporated herein by reference.
BACKGROUND OF THE INVENTION
• 1. Technical Field
• The present invention is directed to a manner in which a processing system schedules the running of threads and the like. More particularly, the invention is directed to a system having adaptive partition scheduling for critical process threads.
• 2. Related Art
• The kernel of an operating system should be capable of dividing up CPU resources so that each thread that is active in the system obtains an adequate amount of CPU time to properly execute the corresponding process. To this end, the kernel may implement a scheduling system that determines how the available CPU time is allocated between multiple threads.
• There are at least three types of process scheduling systems: a FIFO scheduling system; a round-robin scheduling system; and a sporadic scheduling system. In each system, a priority value is assigned to each thread of a process that is executed by the CPU. High priority values are assigned to threads that may be important to the operation of the overall system while threads that may be less important to the operation of the system have lower priority values. Whether the scheduling system gives a thread access to the CPU also depends on the state of the thread. For example, a thread may be ready or blocked (although other states also may be used). A thread is ready when it is capable of being executed in that all conditions needed for it to run have been met. In contrast, a thread is blocked when it tries to initiate an operation that cannot be completed immediately and must wait for the completion of some event before execution of the thread may continue.
• In a FIFO scheduling system, the currently executing thread continues to use all of the CPU time until it gives up the CPU by blocking, it finishes execution, or it is preempted by a higher priority thread. Once one of these criterion are met, the FIFO scheduling system allocates the CPU to the highest priority process/thread that is in a ready state. Generally, there is one ready queue for each priority level.
• A round-robin scheduling system uses an additional parameter, a timeslice, to allocate CPU time to a thread. A timeslice is an amount of time during which a thread is allowed to access the CPU. In a round-robin scheduling system, the currently executing thread continues to use all of the CPU time until the occurrence of one of the following events: 1) the currently executing process blocks; 2) the currently executing process finishes; 3) the currently executing process is preempted by a higher priority thread; or 4) the currently executing process uses up its timeslice. Once the currently executing process blocks or uses up its timeslice, it is put at the back of the ready queue for its priority level.
• Sporadic scheduling is somewhat similar to round-robin scheduling. In a sporadic scheduling system, the currently executing process continues to use all of the CPU time until the occurrence of one of the following events: 1) the currently executing process blocks; 2) the currently executing process finishes; 3) the currently executing process is preempted by a higher priority thread; or 4) the currently executing process uses up a capped limit on the execution time assigned to the thread within a given period of time. The capped limit is known as a budget, while the given period of time in which this budget may be used is known as the replenishment period. In operation, the budget for a thread is replenished upon expiration of the replenishment period. Once the currently executing process blocks, it is put at the back of the ready queue for its priority level. However, if the currently executing process uses up its budget within the replenishment period, its priority level is reduced by a predetermined value and it is placed at the back of the ready queue for this lower priority level. The priority level of the process/thread may be returned to its original value in response to a number of different conditions.
• In certain operating systems, such as those available from QNX Software Systems in Kanata, Ontario, each thread in the system may run using any of the foregoing scheduling systems. Consequently, the scheduling systems are effective on a per-thread basis for all threads and processes on a node. Each thread is assigned to a particular scheduling system type through the operation of the process/thread itself. This provides the software designer with a significant degree of design flexibility, but also involves a need for coordination between software designers implementing code for the same system. This coordination includes the assignment of priorities to the different threads as well as the scheduling system type assigned to each thread.
• Some available operating systems apply scheduling on a global basis. One such global scheduling system is known as fair-share scheduling. In a fair-share scheduling system, CPU usage may be equally distributed among system users, groups, or processes. For example, if four users (A,B,C,D) are concurrently executing one process each, the fair-share scheduler will logically divide the available CPU cycles such that each user gets 25% of the whole (100%/4=25%). If user B starts a second process, each user will still receive 25% of the total cycles, but both of user B's processes will each receive 12.5% of the total available CPU time. On the other hand, if a new user starts a process on the system, the scheduler will reapportion the available CPU cycles such that each user gets 20% of the whole (100%/5=20%).
• Another layer of abstraction allows partitioning of users into groups, and application of the fair share system to the groups as well. In this case, the available CPU cycles are divided first among the groups, then among the users within the groups, and then among the processes for that user. For example, if there are three groups (1,2,3) containing three, two, and four users respectively, the available CPU cycles may be distributed as follows: 100%/3 groups=33.3% per group Group 1: (33.3%/3 users)=11.1% per user Group 2: (33.3%/2 users)=16.7% per user Group 3: (33.3%/4 users)=8.3% per user. Other percentage distributions among the groups also may be used.
• One manner of logically implementing fair-share scheduling strategy is to recursively apply a round-robin scheduling strategy at each level of abstraction (processes, users, groups, etc.). In round robin scheduling, threads of equal importance or priority take turns running. They each run for intervals, or timeslices, that are the property of each thread or group of threads.
• While the foregoing scheduling systems have advantages in different applications, they may experience deficiencies when used in certain system applications. For example, when per-thread scheduling systems are used in real-time systems where the latencies of a process/thread have been planned solely through the assignment of priority levels, very long latencies for low-priority threads may occur. Malicious software processes may configure themselves for high priority execution and thereby preempt proper scheduling of lower priority threads. This problem also may occur, for example, during system development when a high priority thread malfunctions and enters an infinite loop. Global fair-share scheduling systems may avoid such problems, but lack the responsiveness needed for use in a real-time system. Therefore, a need exists for a scheduling system that may effectively allow high-priority threads to operate on a real-time basis while concurrently providing some sort of fair-share CPU access to all threads.
SUMMARY
• A system is set forth that includes a processor, one or more memory storage units, and software code stored in the one or more memory storage units. The software code is executable by the processor to generate a plurality of adaptive partitions that are each associated with one or more process threads. Each of the plurality of adaptive partitions has a corresponding processor time budget. One or more of the process threads are designated as critical threads. Each adaptive partition associated with a critical thread is assigned a corresponding critical time budget. The software code also includes a scheduling system that is executable by the processor for selectively allocating the processor to run the process threads based, at least in part, on the processor time budgets of the respective adaptive partitions. The scheduling system may allocate the processor to run a critical thread based on the available critical time budget of the associated adaptive partition even when the processor time budget of the associated adaptive partition has been exhausted. In one example, the scheduling system functions so that it only bills the critical time budget of an adaptive partition for time used to run an associated critical thread when the processor is overloaded and the critical time budget for the adaptive partition is concurrently exhausted. Methods of implementing such a system are also set forth.
• Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views.
• FIG. 1 is a schematic block diagram of one embodiment of a system that may execute a process scheduler in accordance with the teachings of the present invention.
• FIG. 2 is a diagram illustrating a number of different interrelated processes that may be used to set up a process scheduler that employs adaptive partitions.
• FIG. 3 is a diagram of one exemplary process scheduler that employs a plurality of adaptive partitions with their associated threads and thread priorities.
• FIG. 4 is a diagram of a further exemplary process scheduler that employs a plurality of adaptive partitions with their associated threads and thread priorities, where the process scheduler is operating under different conditions than those shown inFIG. 3.
• FIG. 5 is a diagram of an exemplary process scheduler that employs a plurality of adaptive partitions with their associated threads and thread priorities, where at least one of the ready threads has been designated as a critical thread.
• FIG. 6 is a flow diagram showing a plurality of interrelated processes that may be used to implement the process scheduler in a software environment in which there are sending threads and receiving threads.
• FIG. 7 is a diagram illustrating the operation of the process scheduler described in connection withFIG. 6.
• FIG. 8 is a flow diagram showing a plurality of interrelated processes that may be used to schedule the running of threads associated with the various adaptive partitions.
• FIG. 9 is a flow diagram showing a plurality of interrelated processes that may be used to determine whether the process scheduler bills the guaranteed budget or critical budget associated with the running thread.
• FIG. 10 is a flow diagram showing a plurality of interrelated processes that may be used to calculate the relative budget used by an adaptive partition, where the value of the relative budget used may be employed in the process shown inFIG. 8.
• FIG. 11 is a flow diagram showing a plurality of interrelated processes that may be used to schedule the running of threads that access the same mutexes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIG. 1 is a schematic block diagram of asystem100 that may execute a process scheduler employing an adaptive partitioning of process threads.System100 includes a central processing unit105 (“CPU”) that may access software code stored inmemory110.CPU105 also may be disposed to access various devices/system components through an I/O interface115. The devices/system components may include, for example, sensors, human interface devices, network nodes, printers, storage devices, or the like. The processors in a symmetric multiprocessing system, regardless of the number, may be considered in the same manner as a single processor and are likewise included in the scope of the representation byblock105.
• Memory110 may be used to store, among other things, the software code that defines the functions that are to be executed by thesystem100. Althoughmemory110 is shown as a single unit, it may be implemented as multiple memory units of the same or different memory type. For example,memory110 may be implemented with multiple flash memory devices. Alternatively, or in addition,memory110 may be implemented with one or more flash memory devices and one or more hard disc storage devices. It will be recognized that a substantial number of alternative memory device combinations may be used to implementmemory110.
• Some of the software code that may be stored inmemory110 and executed byCPU105 is identified inFIG. 1. The identified software code shown here includes anoperating system120 and one ormore software applications125. In this example, aprocess scheduler130 anddevice drivers135 are included as members of theoperating system120. Theprocess scheduler130 anddevice drivers135, however, also may be implemented as software modules that are separate from theoperating system120.Software applications125 may be used to define the high-level functions thatsystem100 is to perform.Device drivers135 may be used to provide a hardware abstraction layer through whichsoftware applications125 communicate with the hardware components of thesystem100. The hardware components may include the components accessed through I/O interface115.
• Process scheduler130 comprises the executable software code that is used to allocate the processing time of the CPU105 (“CPU time”) to each thread of thesystem100. The CPU time may be allocated so that each thread obtains an adequate amount of CPU time to properly execute the corresponding process.
• FIG. 2 is a flow chart showing a number of interrelated operations that may be used to implement theprocess scheduler130. The flow chart ofFIG. 2 illustrates many of the values and operational characteristics used in theprocess scheduler130. Some values or operational characteristics may be fixed as a result of user choices during the design process, while other values or operational characteristics are provided through configuration data provided by a user and/or through software programming of thesystem100.
• As shown, theprocess scheduler130 creates a number of different adaptive partitions at block205. Each adaptive partition constitutes a virtual container for scheduling attributes associated with a set of process threads that have been grouped together by theprocess scheduler130. Threads that work toward a common or related function may be assigned to the same adaptive partition. In object-oriented systems, the adaptive partitions may be generated as instances of an adaptive partition class that includes corresponding scheduling methods and attributes. Each of the adaptive partitions generated at block205 is uniquely identified for further access by theprocess scheduler130.
• The number of partitions generated by theprocess scheduler130 may be initiated through the use of configuration parameters. The configuration data may be provided by user initiated commands or through programs that interface with theprocess scheduler130.
• Atblock210, the size of the averaging window that will be used by theprocess scheduler130 is calculated. As will be set forth in further detail below, the averaging window is the time over which theprocess scheduler130 attempts to keep adaptive partitions at their guaranteed CPU percentages when the system is overloaded. A typical time is 100 milliseconds, though other averaging window sizes may be appropriate. The averaging window size may be specified at boot time, and may be respecified any time thereafter as well. Considerations in choosing the size of the averaging window may include:
• • A short duration averaging window size reduces the accuracy of CPU time-balancing.
  • When a short duration averaging window is used, partitions that exhaust their budgets because other partitions are using less than their guaranteed percentage may not have to pay the time back.
  • In some instances, a long duration averaging window size may cause some adaptive partitions to experience runtime delays.
• The size of the averaging window (“windowsize”) may be assigned in terms of milliseconds, which thescheduling process130 converts to clock ticks. A clock tick is the interval between clock interrupts (the system timer). All of the time budgets used by thescheduling process130 may be averaged over the same windowsize.
• Atblock215, thescheduling process130 assigns a guaranteed CPU time budget to each adaptive partition. The guaranteed budget may be assigned as a percentage of the overall available system budget. The sum of all adaptive partitions' CPU percentages in such instances will be 100%. For the purpose of assigning shares of the overall CPU time budget, the processors in a symmetric multiprocessing system, regardless of the number, may be considered in the same manner as a single processor.
• The guaranteed budget used for each adaptive partition may be determined in a number of different manners. For example, the CPU time used by each partition under several different load conditions may be measured and then used to construct a graph of load versus CPU time consumed by each partition. Measurements also may be made under overload conditions. This information may be used to balance the needs of the various threads contained in each partition under the various conditions and assign the appropriate guaranteed CPU time budgets. The measurements also may be used to dynamically vary the guaranteed CPU time budgets with respect to CPU load conditions. For example, theprocess scheduler130 may operate in accordance with different operating modes in response to different operating conditions. While operating in a particular mode, theprocess scheduler130 employs a unique set of adaptive partition parameters. The availability and parameters associated with a particular mode may be specified at boot time. An application programming interface (“API”) at run-time may be used to switch modes as needed. For example, a first set of guaranteed CPU time percentages may be employed during startup while a second set of guaranteed CPU time percentages may be employed during normal operations after system startup has been completed.
• A priority is assigned to each thread and each thread is associated with a respective adaptive partition atblock220. Functionally-related software may be assigned to the same adaptive partition. This effects a hybrid process scheduling system in which the priority assigned to a thread as well as the guaranteed CPU time percentages of the adaptive partitions are used in the scheduling decisions executed by theprocess scheduler130.
• In assigning the threads to respective adaptive partitions, adaptive partition scheduling may be used as a structured way of deciding when the running of a particular function of the system will be inhibited. When used in this manner, separate threads may be placed into different adaptive partitions based on whether the threads should be starved of CPU time under a particular set of circumstances. For example, suppose thesystem100 is designed to operate as a packet router. Some of the processes that may be executed by a packet router include 1) routing packets, 2) collecting and logging statistics for packet routing, 3) route-topology protocols with peer routers, and 4) collecting logging and route-topology metrics. In such instances, the threads of these processes may be assigned to two adaptive partitions: one for threads associated with routing and one for threads associated with the topology of the network. When the system is overloaded (i.e., there is more outstanding work than the machine may possibly accomplish), there may be a need to determine which applications are to be run slower. To this end, it may be preferable to route packets as opposed to collecting routing metrics if the CPU does not have enough resources to execute threads for both routing and metrics. It also may be reasonable to run the threads associated with network topology protocols, even when CPU resources are limited. Under these circumstances, it may be preferable to employ three adaptive partitions as opposed to the two adaptive partitions initially considered. The three adaptive partitions, along with exemplary guaranteed budgets, may include:
• • an adaptive partition for routing packets (80% share);
  • an adaptive partition for topology protocols (15% share), but with maximum thread priorities higher than the threads in the adaptive partition for routing packets; and
  • an adaptive partition (5% share) for logging of both routing metrics and topology-protocol metrics.
• In this case, adaptive partition scheduling has been used to reorganize various system functions so that certain functions are given priority during high CPU loads, while still ensuring that all system functions are given CPU execution time. Threads associated with routing and threads associated with logging routing metrics have been associated with separate adaptive partitions despite the fact that they are functionally related to routing operations. Similarly, two functionally unrelated components, routing metric logging and topology metric logging, have been associated with the same adaptive partition. This manner of assigning the various threads to different partitions enables theprocess scheduler130 to reduce CPU time usage by the logging threads under high CPU load conditions and give priority to routing threads and topology protocol threads while still conducting metrics logging.
• Atblock225, a determination may be made as to which threads of the system will be allowed to run in a critical state. Designating a thread as critical gives it the ability to run in a manner that approximates a real-time system, even when the guaranteed budget for the adaptive partition budget might otherwise be exceeded. When a critical thread associated with a particular adaptive partition is run despite the lack of guaranteed budget for the adaptive partition, the adaptive partition is said to have gone into short-term debt. Critical threads may be associated with the various partitions, for example, at boot time. Critical threads are discussed in further detail below.
• Each adaptive partition that is associated with a critical thread is assigned a critical time budget atblock235. The critical time budget may be specified, for example, in time units, such as milliseconds. In the exemplary system, the critical time budget is the amount of CPU time available to all critical threads associated with a given adaptive partition above that partition's guaranteed time budget during an averaging window. By employing critical designations and critical time budgets, a critical thread generally has an opportunity to run on the CPU even if its associated adaptive partition has exhausted its guaranteed budget. This will occur as long as the partition still has critical time budget available. Critical threads may provide the ability for real-time behavior within these partitions.
• Various policies that theprocess scheduler130 must follow may be optionally assigned to thesystem100 atblock240. For example, a bankruptcy policy may be applied to one or more of the adaptive partitions to determine how thesystem100 and/orprocess scheduler130 handles a bankrupt state of the adaptive partition. Bankruptcy of a critical adaptive partition occurs when the adaptive partition has exhausted both its guaranteed CPU time budget and critical time budget over the duration of the averaging window. As a further example,system100 may execute an overload notification policy that allows a process to register with theprocess scheduler130 so that it is notified when a system overload occurs. A system overload occurs, for example, when all of the ready threads cannot be executed on the CPU over the duration of the averaging window. A process may register to be informed of an overload condition when thesystem100 enters and/or leaves the overload state. Applications may use this overload notification to gracefully degrade their service, for example, by skipping less important functions, or by reducing the precision of computation. Adaptive partitions may go over budget when some other adaptive partition is sleeping, as will be set forth below. This is not by itself necessarily considered to be a system overload, and therefore does not require triggering of the overload-notification policy.
• At block245, theprocess scheduler130 is configured with data corresponding to the foregoing states, values, and/or assignments provided at blocks205 through240. As noted above, these states, values and/or assignments may be provided for use in thesystem100 in a number of different manners, such as, by the system designer, by the system user, through other software programs, etc.
• Block250 represents execution of the threads in accordance with the configuration data of block245. The attributes of the various adaptive partitions may be dynamic. To this end, the parameters set forth in one or more of the foregoing blocks may be changed in response to system requirements, system state, changes in system functions, etc., as represented by the flowline returning to block205.
• The threads insystem100 also may vary dynamically over time. For example, a thread or group of threads associated with an adaptive partition may spawn, or generate, other threads during operation. The originating thread may be referred to as a parent thread while a spawned thread may be referred to as a child thread.Process scheduler130 may be configured so that child threads inherit the adaptive partition of their parent thread automatically. Alternatively, or in addition, an API may be provided that will allow spawning threads into other adaptive partitions. Such an API may be made available only to code with sufficient privilege. For example, a system application launcher may have such privileges.
• FIG. 3 illustrates one manner in which theprocess scheduler130 may operate under normal load conditions in which none of the partitions exceeds its CPU budget. In this example, theprocess scheduler130 has generated threeadaptive partitions301,302, and303.Adaptive partition301 may be associated with thethreads305,306,307, and308, of a multimedia application.Adaptive partition302 may be associated with thethreads315,316,317,318, and319 of a Java application.Adaptive partition303 may be associated with thethreads320,325,330,335, and340 of a system logging application. The threads305-345 have various scheduling priorities, denoted in parentheses inFIG. 3, that may be independent of the guaranteed budget of the associated adaptive partition.
• In operation, each adaptive partition301-303 and thread305-345 may assume different operative states. Adaptive partitions301-303, for example, may operate in an active state or a sleep state. In the active state, the scheduling attributes of the adaptive partition may be used to schedule CPU time for the associated threads. A sleep state occurs when there are no ready threads associated with the adaptive partition. In such instances, theprocess scheduler130 effectively treats the adaptive partition as non-existent.
• Threads may assume, for example, a running state, a ready state or a blocked state. A thread is in the running state while it is being executed by the CPU. It is in a ready state when a set of conditions have been met that render the thread fully prepared for execution by the CPU at a time determined by theprocess scheduler130. A thread is in the blocked state while the thread waits for the occurrence of one or more events. While in the blocked state, the thread is not ready to consume any CPU resources. Once the events awaited by the thread occur, the thread may become unblocked and enter the ready or running state.
• The adaptive partitions301-303 and corresponding threads305-345 can be used to describe the operation of theprocess scheduler130 during various load conditions. In this example, theprocess scheduler130 makes the CPU available to executeready threads308,315, and345 assigned to eachadaptive partition301,302, and303, based on the priority of the ready threads. Under normal load conditions, the highest-priority thread in thesystem100 will run immediately when it becomes ready. Whether a thread is ready may be indicated to theprocess scheduler130 in a number of different manners including, for example, through the occurrence of an interrupt event or the like. In the illustrated example, the highest priority ready thread isthread345, which has a priority of17.Thread345 will continue to operate in a running state until it is finished, blocked, or until the budget foradaptive partition303 is exhausted. Under heavy load, if an adaptive partition exceeds its CPU budget, then its highest-priority thread does not run until the partition once again has time available in its CPU budget. This is a safeguard on thesystem100 that divides insufficient CPU time among thepartitions301,302, and303. In this state, the processor runs the highest-priority thread in an adaptive partition with CPU time remaining in its guaranteed CPU time budget.
• When an adaptive partition enters a sleep state, theprocess scheduler130 allocates the CPU budget of the sleeping partition to other active adaptive partitions—even if the other active adaptive partitions have exceeded their budget. For example, ifadaptive partition303 enters a sleep state, theprocess scheduler130 allocates the budget foradaptive partition303 toadaptive partition302, sinceadaptive partition302 has the highest priorityready thread315. If two or more adaptive partitions have threads with the same highest priority, theprocess scheduler130 divides the free time in proportion to the other adaptive partitions' percentages. This allocation assists in preventing long ready-queue delay times in the case where two adaptive partitions have the same priority.
• In the example ofFIG. 4, there are threeadaptive partitions401,402, and403, with 70%, 20% and 10% CPU budget guarantees, respectively. Further, eachadaptive partition401,402, and403, includes aready thread408,415, and445, having a priority of14. Ifadaptive partition401 enters a sleep state through a blocking ofthread408, theprocess scheduler130 allocates all of the available CPU time toadaptive partitions402 and403 in a 2:1 ratio, the ratio corresponding to their original CPU budget allocations. Ifadaptive partition401 is in a sleep state for a short time, then theprocess scheduler130 may ensure thatpartition401 later receives CPU time at its guaranteed CPU time budget by reallocating the CPU resources so thatadaptive partitions402 and403 pay back the CPU time that each utilized at the expense ofpartition401. Ifadaptive partition401 is in a sleep state for a long time, then some or all of the time used byadaptive partitions402 and403 may become free. Whether an adaptive partition is in a sleep state for a short time or a long time can be determined in various manners. For example, an adaptive partition can be said to be in a sleep state for a short time when it is in the sleep state for a duration of time that is less than (windowsize)−(budget percentage*windowsize) milliseconds within one averaging window.
• If all adaptive partitions are at their CPU budget limits, then theprocess scheduler130 may specify running of the highest-priority thread in thesystem100. If two adaptive partitions have threads with the same highest priority, then the adaptive partition that has used the smallest fraction of its budget may be run. This manner of operation may be used to prevent long ready-queue delays that would otherwise occur. In the example shown inFIG. 4, the window size may be 100 ms,adaptive partition401 is allotted 70% of the CPU budget and has used 40 ms,adaptive partition402 is allotted 20% of the CPU budget and has used 5 ms, andadaptive partition403 is allotted 10% of the CPU budget and has used 7 ms. All partitions have a ready thread atpriority14. In this situation,thread415 ofadaptive partition402 is run because its relative fraction free is 5 ms/20 ms, or 0.25, while the relative fraction free foradaptive partition401 is 40 ms/70 ms or 0.57 and 7 ms/10 ms or 0.70 foradaptive partition403.
• If an adaptive partition has exhausted the assigned CPU budget and one or more of its ready threads are designated as critical, then theprocess scheduler130 may allow the adaptive partition to use its critical CPU budget to run the critical threads. The critical time budget is the amount of CPU time that theprocess scheduler130 allocates to an adaptive partition to run all critical threads associated with the adaptive partition. This critical time budget constitutes CPU time that theprocess scheduler130 allocates to the adaptive partition the partition's normal budget during an averaging window. Consequently, a critical thread may run even if the adaptive partition with which it is associated is out of budget, as long as the adaptive partition has not exhausted its critical time budget.
• FIG. 5 illustrates a system having twoadaptive partitions501 and502.Threads505,506,507, and508 are associated withadaptive partition501, whilethreads515,516,517,518, and519 are associated withadaptive partition502.Adaptive partition501 may comprise threads that are associated with, for example, an airbag notification process in a vehicle.Threads505 and508 ofadaptive partition501 have been designated as critical threads. However, onlythread508 is in a ready state.
• In this example,adaptive partition501 has exhausted its guaranteed CPU time budget. Nonetheless,critical thread508 may be allowed to run because of the importance that has been placed on it through the critical designation. Consequently, theprocess scheduler130 may allocate CPU time tocritical thread508 provided there is still CPU time in the critical time budget ofadaptive partition501.
• When theprocess scheduler130 schedules the running of a critical thread, such asthread508, the process scheduler bills the thread's run time against the available guaranteed CPU time budget of the thread's associated adaptive partition. However, theprocess scheduler130 counts the CPU time used by the critical thread against the critical time budget of the adaptive partition only if theprocess scheduler130 would not have otherwise run the critical thread. To this end, CPU time used in running a critical thread is not counted against the critical time budget of the associated adaptive partition when 1) the system is not overloaded, or 2) the system is overloaded, but one or more adaptive partitions may not be exhausting their guaranteed CPU time budgets.
• A critical thread may remain in a critical running state until it enters a blocking state. That is, it may leave the running or ready state as is the case with any other thread. As noted above, this may occur while the thread is waiting for a message, interrupt notification, etc. The criticality of a thread, or billing to its adaptive partition's critical time budget, may be inherited along with the adaptive partition during operations which trigger priority inheritance.
• The short-term debt is bounded by the critical time budget specified for the partition. Over time, the partition may be required to repay short-term debt. A critical thread that exceeds the critical time budget of the adaptive partition may be considered to drive the associated adaptive partition into bankruptcy. Bankruptcy may be handled as an application error, and the designer may specify the system's response. Exemplary choices for a response include: 1) forcing the system to reboot; 2) notifying an internal or external system watchdog; and/or 3) terminating and/or notifying other designated processes. The system may add an entry to a log or the like if an adaptive partition exhausts its critical time budget. When the budgets for the adaptive partitions are dynamically altered (through, for example, a mode change, an API call to modify CPU percentages, or the like), theprocess scheduler130 may impose a delay before testing an adaptive partition for bankruptcy. This allows the budgets to stabilize before an adaptive partition may be declared bankrupt.
• The designation of a thread as critical may occur in a number of different manners. For example, the system may automatically mark threads that are initiated by an I/O interrupt as critical. The system also may specify a set of additional applications or operating system notification events, for example, timers, which may mark their associated handler threads as critical. An API also may be used to mark selected threads as critical. Still further, child threads of critical parent threads may be automatically designated as critical.
• Theprocess scheduler130 also may be adapted for use in client/server systems in which messages are passed from one or more sending/client threads for receipt and/or processing by one or more receiving/server threads.FIG. 6 shows a number of interrelated processes that may be used to implementprocess scheduler130 in such a client/server environment. At block605, a client thread in a first adaptive partition sends a message to a server thread in a second adaptive partition. At block607, a check is made to determine whether the targeted receiving thread is busy. When a client thread sends a message to a server thread, the server thread that receives the message may inherit the priority of the sending thread. This prevents priority inversion, since the server thread is doing work on behalf of the sending client. Inheriting of the priority level of the sending thread by the server thread is shown at block610 and occurs, for example, when the targeted receiving thread is not busy. The process scheduler also may assign the same critical status of the client thread to the server thread at block610. Atblock615, theprocess scheduler130 may associate the server thread with the same adaptive partition that is associated with the client thread.
• FIG. 7 illustrates a system that may be used to explain some aspects of the operations shown inFIG. 6. In this example, there are threeadaptive partitions701,702, and703.Adaptive partition702 may includeserver threads720 and725 of the type run, for example, by the processes of a file system. The attributes assigned toadaptive partition702 may vary with the design of the system. However, in this example,adaptive partition702 has been generated with a CPU time budget of zero, andthreads720 and725 have been assigned a default priority of7.Adaptive partition701 may comprise a number ofdifferent threads705,710, and715, wherethread715 constitutes a client thread that sends messages to one or more server threads ofadaptive partition702. Similarly,adaptive partition703 may comprise a number ofdifferent threads730,735,740, and745, wherethread745 constitutes a client thread that sends messages to one or more server threads ofadaptive partition702.
• As shown by line750 ofFIG. 7,client thread715 has passed a message that is received or otherwise processed bythread720 ofadaptive partition702. Similarly,client thread745 ofadaptive partition703 has passed a message that is received or otherwise processed bythread725 ofadaptive partition702, as indicated byline755. When the message transfers750 and755 occur, theprocess scheduler130 associates each server/receiving with the adaptive partition of the thread that sent the message. In this case,server thread720 is temporarily associated withadaptive partition701, as indicated byline760, and is assigned the same priority,14, asthread715. Likewise,server thread725 is temporarily associated withadaptive partition703, as indicated byline765, and is assigned to the same priority,12, asthread745. Boththreads720 and725 may be placed in a ready state, whilethreads715 and745 may be placed in a blocked state as the respective messages are processed. Oncethread720 has completed processing the message received fromthread715,thread720 may return to its original state where it is associated withadaptive partition702 with a default priority of7. Also,thread725 may return to its original state where it is associated withadaptive partition702 with a default priority of7 once it has completed processing of the message received fromthread745.
• Sometimes, a client thread may attempt to communicate with a server thread that is busy processing one or more messages that have been previously received from other client threads. For example, ifthread740 ofadaptive partition703 becomes unblocked and attempts to send a message toserver thread725 whileserver thread725 is busy processing one or more prior messages received fromthread745,server thread725 typically will be unable to respond tothread740 until it has completed processing the prior messages fromclient thread745. In such instances, theprocess scheduler130 temporarily may raise the priorities of one or more server threads that, for example, wait on the same connection path as the client thread. The query and action corresponding to these operations are illustrated atblocks607 and625 ofFIG. 6. As applied to the system ofFIG. 7, the connection path between threads assigned toadaptive partition703 and threads assigned toadaptive partition702, for example, may be assigned the same identification name/number. As a result, the priority ofserver thread725 may be raised in an attempt to reduce the latency that may otherwise occur beforeserver thread725 is available to process the message fromclient thread740. Depending on the nature of the threads inadaptive partition702, the priority levels of multiple server threads may be raised.
• Atblock630 ofFIG. 6, theprocess scheduler130 operates to bill the execution time for eachthread720 and725 in the appropriate manner. The appropriate manner of billing the execution time may vary. One manner includes applying the execution time of the receiving thread against the CPU budget and/or critical CPU budget of the adaptive partition associated with the sending thread. In the example ofFIG. 7, the execution time used bythread720 in responding to a message sent bythread715 is counted against the CPU budget and/or critical CPU budget ofadaptive partition701. Similarly, the execution time used bythread725 in responding to a message sent bythread745 is counted against the CPU budget and/or critical CPU budget ofadaptive partition703.
• System components, such as filesystems, device drivers, and the like may be assigned a guaranteed budget of zero. In such instances, the CPU time used by the threads associated with the system component is billed to their clients. However, sometimes theprocess scheduler130 finds out too late which threads a particular system component thread has been ultimately working for. As a result, theprocess scheduler130 may not be able to bill the running of the threads of the system components in a timely manner and/or to the proper adaptive partition. Additionally, some system components, such as device drivers, may have background threads (e.g. for audits or maintenance) that require budgets that cannot be attributed to a particular client. In those cases, the system designer may measure the background operations and unattributable loads associated with the various system components. The resulting measurements may be used to provide non-zero budgets to the adaptive partitions associated with the threads of the various system components.
• In operation, theprocess scheduler130 may do more than simply direct the running of the highest priority ready thread associated with an adaptive partition having guaranteed CPU time left in its budget. For example, when all adaptive partitions have exhausted their guaranteed CPU time budgets at approximately the same time, then theprocess scheduler130 may direct the running of the highest priority thread in the system irrespective of the attributes of the associated adaptive partition. Also, when adaptive partitions have threads of the equal highest priorities, theprocess scheduler130 may assign CPU time using the ratio of their guaranteed CPU time percentages. Finally, critical threads may be run even if their adaptive partition is out of budget, provided the adaptive partition still possesses an amount of its critical time budget.
• Process scheduler130 may employ one or more ordering functions, f(ap), associated with each adaptive partition, ap, in its scheduling determinations. Ordering functions may be calculated in a variety of different manners. The results obtained by calculating the ordering functions may be compared with one another to determine how theprocess scheduler130 will scheduled the threads associated with the various adaptive partitions of the system.
• In calculating the ordering functions, f(ap), a number of different variables may be used. A few of the variables are described here in connection with one example. In the following example, let “is_critical(ap)” be a boolean variable. The value of “is_critcal(ap)” depends on 1) whether the adaptive partition, ap, has available critical budget, and 2) whether the highest priority ready thread in the adaptive partition, ap, has been assigned a critical state. Let “has_budget(ap)” be a boolean variable that indicates whether an adaptive partition, ap, has consumed less CPU time than its guaranteed CPU time budget during the last averaging window. Let “highest_prio(ap)” be an integer variable that indicates the highest priority of all ready-to-run threads in an adaptive partition, ap. Let “relative_fraction_used(ap)” be a real number variable that corresponds to the ratio of the number of microseconds of CPU time consumed by the adaptive partition, ap, during the last averaging window, divided by the budget of the adaptive partition, ap, when expressed, for example, in microseconds. Finally, let b(ap) be a boolean variable corresponding to the current rate of CPU time consumption of threads in the adaptive partition, ap. More particularly, b(ap) may be assigned a logical true value if, given the current rate of CPU time consumption by the threads associated with the partition, ap, the value of has_budget(ap) also would be a logical true value at the time theprocess scheduler130 would likely be called upon to again schedule a thread associated with the adaptive partition. Otherwise, b(ap) may be assigned a logical false value. It will be recognized that other variables, or less than all of the foregoing variables, may be used to calculate and ordering function f(ap). Which variables are used may be dependent on the system designer and/or end-user.
• The value of b(ap) may be calculated in a number of different manners. For example, let the variable t indicate the current time in a high-resolution counter, and a tick be the length of time between regular events during which the process scheduler examines all partitions. The period of the tick should be less than the size of the averaging window (“windowsize”). Let the function cpu_time_used(t1,t2) correspond to a real value of the CPU time used by the threads of partition, ap, between absolute times t1 and t2. Further, let budget(ap) correspond to the time value of the guaranteed budget for the partition, ap. The value for b(ap) then may be calculated using the following equation:
  b(ap)=Boolean (cpu_time_used(now, now-windowsize)−cpu_time_used(now-windowsize+tick, now-windowsize)<budget(ap)).
• One manner of calculating an ordering function, f(ap) using the foregoing variables is shown inFIG. 8. The illustrated operations may be executed for each adaptive partition, ap, used in thesystem100. As shown, theprocess scheduler130 determines whether the partition has any threads that are ready to run atblock800. If there are no ready threads associated with the adaptive partition, ap, the ordering function, f(ap), for the adaptive partition may be assigned the values f(0,0,0,0), at block802 and calculation of the ordering function for the next adaptive partition may be initiated at block803. Theprocess scheduler130 determines if the adaptive partition, ap, has critical CPU budget available atblock805 and, if so, whether the highest priority ready thread in the adaptive partition, ap, has been assigned a critical state. Based on this determination, theprocess scheduler130 assigns the appropriate logical state to the “is_critical(ap)” variable atblock810. At block813, theprocess scheduler130 evaluates the CPU budget used by the adaptive partition during the last averaging window. At block815, theprocess scheduler130 determines if the adaptive partition has used less CPU time than its guaranteed CPU time budget. Based on this determination, theprocess scheduler130 assigns the appropriate logical state to the “has_budget(ap)” variable atblock820. The relative ratio of CPU budget time used during the last averaging window is calculated at block830 by taking the value obtained at block813 and dividing it by the guaranteed CPU budget time for that adaptive partition. This value is assigned to the “relative_fraction_used(ap)” variable at block835.
• Atblock840, theprocess scheduler130 calculates one or more values corresponding to the current rate of CPU time consumption by threads associated with the adaptive partition. These values are used to assign the appropriate logical state to the b(ap) variable atblock845.
• Using all or a subset of the foregoing variables, the ordering function, f(ap), for the given adaptive partition, ap, is calculated atblock850. In this example, the ordering function, f(ap), is calculated using the ordered values (x,a,y,z), where x=is_critical(ap) OR has_budget(ap); a=(Not x) AND b(ap); y=highest_prio(ap); and z=1−relative_fraction_used(ap). In calculating the ordering function, f(ap), the value of x is given more significance than the values of a, y, or z, the value of a is given more significance than the values of y or z, and the value of y is given more significance than the value of z.
• Theprocess scheduler130 runs the highest priority thread of the adaptive partition having the largest f(ap) as shown atblock905 ofFIG. 9. However, theprocess scheduler130 must determine whether the running time for the thread is to be billed to the critical budget of the adaptive partition or solely to the guaranteed budget. To this end, theprocess scheduler130 may compute another function, fcritical(ap), using one or more of the foregoing variables. In this example, fcritical(ap) is calculated using the ordered values (w,d,y,z), where w=has_budget(ap); d=(NOT w) AND b(ap); y=highest_prio(ap); and z=1−relative_fraction_used(ap). In the calculation of fcritical(ap), the value of w is given more significance than the values of d, y, or z, the value of d is given more significance than the values of y or z, and the value of y is given more significance than the value of z. This calculation is shown atblock910. A comparison between the fcritical(ap) and f(ap) values for the adaptive partitions is executed atblock915. If the value of fcritical(ap) is less than the value of f(ap), then the running time for the thread is billed to the critical budget of the adaptive partition atblock920 as well as to the guaranteed budget atblock925. If the value of fcritical(ap) is greater than or equal to the value of f(ap), then the running time for the thread is solely billed to the guaranteed budget of the adaptive partition atblock925. Any calculations used by theprocess scheduler130 should ensure that the critical budget for the adaptive partition is only used if the highest priority critical thread associated with that adaptive partition would not have been selected to run byprocess scheduler130 had the thread or the partition not been critical.
• FIG. 10 shows a number of different interrelated processes that may be used to execute a method for calculating the relative ratio of CPU budget time consumed during the last averaging window, as described in block830 ofFIG. 8. The relative fraction CPU budget time consumed by an adaptive partition is, for example, the number of microseconds that threads associated with the adaptive partition ran during the last averaging window divided by its share of the averaging window in microseconds. Alternatively, this may be expressed as (total_CPU_time_consumed)/(windowsize*percentage). To reduce the potential need for floating-point division, theprocess scheduler130 may compute a number that has substantially the same ordering properties as (total_CPU_time_consumed)/(windowsize*percentage) for each adaptive partition. Thus, a constant c(a) may be pre-computed so that the adaptive partition with the highest (total_CPU_time_consumed)*c(ap) also is the adaptive partition with the highest (total_CPU_time_consumed)/(windowsize*percentage).
• The function c(ap) may be precalculated during, for example, system startup, and whenever the guaranteed CPU budgets are reallocated between the various adaptive partitions of the system. Atblock1010, the CPU budget percentage for each adaptive partition are determined, for example, at start-up. Atblock1015, the system may compute, for each adaptive partition, a factor, q(ap). The value of q(ap) may be calculated, for example, as the product of the percentage CPU budgets of all the other adaptive partitions. Atblock1020, a scaling factor is calculated. In this example, if the maximum averaging error is max_error (e.g. 0.005 for ½ a percent), then k=min(list of q(ap))*max_error. A constant scaling factor c(ap) is calculated atstep1025. In this example, c(ap) is calculated as c(ap)=q(ap)/k. The value, (total_CPU_time_consumed)*c(ap) has the same ordering properties as (total_CPU_time_consumed)/(windowsize*percentage) within an error tolerance of max_error.
• To practically compare the relative fraction used by different adaptive partitions, theprocess scheduler130 may need to multiply the run time of the threads associated with the adaptive partitions by c(ap). However the billed times may be large numbers. If theprocess scheduler130 is to be implemented using single-multiply instructions in these calculations, the billed times may be first scaled choosing a number of most significant bits of the CPU budget time at block1030. The degree of scaling may be set by the value of max_error. However, any reasonable choice for max_error (e.g. ¼ to ½%) can be satisfied by choosing only the most significant 16 bits of the billed run-time. In such instances, the system may be calculating (total_CPU_time_consumed)>>32*c(ap). Atblock1035, the relative budget ratio is calculated as c(ap)*(adaptive partition execution time), where (adaptive partition execution time) constitutes a selected number of the most significant bits of (total_CPU_time_consumed).
• An error tolerance of 0.5% to 0.25% is considered sufficient for an implementation. However, the application may include the notion that for any specified error tolerance, a minimal number of bits is chosen to both represent c(ap), the scaled value of the CPU time executed by adaptive partition ap, during the last averaging windowsize time, and the product of c(ap) and the scaled CPU time. The minimal number of bits is chosen for both representations and executing multiplication functions so that all representations and arithmetic errors are less than or equal to a chosen error tolerance.
• Billing of CPU time to each of the adaptive partition in a system may take place in a number of different manners and may occur many times during the operation of theprocess scheduler130. For example, billing of an adaptive partition may occur whenever 1) a thread starts running from a blocked state, 2) a thread stops running (i.e., when it has been preempted by a higher priority thread, when it has been blocked, or the like), and/or 3) at other times when an accurate accounting of the CPU time is needed by theprocess scheduler130.
• Typically, process schedulers use standard timer interrupts, or ticks, to determine how long a thread has used the CPU. Tick periods are often on the order of one to several milliseconds.
• Theprocess scheduler130, however, may include code that effectively microbills the execution time of the various threads of the system. To this end, a high-resolution hardware and/or software counter having a period substantially less than the tick periods may be employed. Each time a thread starts or stops running, theprocess scheduler130 assigns a timestamp to the associated partition corresponding to the value of the high-resolution counter. The timestamp values may be scaled to a useful common time unit. The differences between the timestamps for adjacent start and stop times of a thread are used to microbill the appropriate adaptive partition.
• The high-resolution counter may be implemented in a number of different manners. For example, some CPUs have a built-in counter that increments at about the clock frequency at which the CPU is run. In such situations, the built-in counter may be used in the microbilling process. In another example, a high-resolution counter may be simulated using software by querying an intermediate state of a programmable count-down timer that, for example, may normally be used to trigger clock interrupts. This may be the same counter used to provide an indication that a tick interval has occurred. In such situations, the timestamps should take into consideration both the counter value and the number of ticks that have occurred from a given reference point in time so that the timestamps accurately reflect the start times and stop times of the individual threads.
• The foregoingprocess scheduler130 also may be used in systems that employ mutexes. Mutexes are used to prevent data inconsistencies due to race conditions. A race condition often occurs when two or more threads need to perform operations on the same memory area, but the results of computations depend on the order in which these operations are performed. Mutexes may be used for serializing shared resources. Anytime a global resource is accessed by more than one thread the resource may have a mutex associated with it. One may apply a mutex to protect a segment of memory (“critical region”) from other threads. The application gives a mutex to threads in the order that they are requested. However, theprocess scheduler130 may be adapted to deal with the problems that occur when a low-priority thread, which may hold the mutex, unreasonably delays access to higher-priority threads that are waiting for the same mutex.
• FIG. 11 shows a method for prioritizing access to a mutex in an adaptive partitioning system, when one thread may hold a mutex, and several other threads may be waiting for the same mutex. When the partition associated with the thread holding the mutex runs out of guaranteed CPU time budget, theprocess scheduler130 may begin billing the run time of the thread holding the mutex to the partition of the thread waiting for the mutex which, of all the threads waiting for the mutex, is most likely to run next. Theprocess scheduler130 also may begin billing the run time of any thread deemed to be working on behalf of the thread holding the mutex to the adaptive partition associated with the thread holding the mutex. A determination is made atblock1110 to identify the thread that is most likely to run next (i.e., the thread that will run after the thread holding the mutex is blocked, finishes, or the like). The waiting thread, which may be waiting for the same mutex as the current thread holding the mutex, may be determined to be “most likely to run next”. Atblock1115, theprocess scheduler130 may raise the priority level of the thread holding the mutex to the priority of the waiting thread which is most likely, of all the waiting threads, to run next. Theprocess scheduler130 may bill the adaptive partition associated with the current thread holding the mutex for its running time while holding the mutex until the adaptive partition's CPU budget is exhausted (reaches zero) at block1120. Atblock1125, the remaining CPU time used by the holding thread is billed to the adaptive partition that is associated with the waiting thread that is most likely to run next.
• The thread “most likely to run next” may be computed by applying, pairwise, a “compare two threads” process repeatedly on pairs of threads in a list of waiting threads. The “compare two threads” process may be executed as follows, where A and B are the two threads to be compared: A function f(ap) is constructed, which includes the ordered values (x,a,y,z). This is the same ordering function f(ap) constructed above. Then, let partition_of(X) mean the partition containing the thread X. Then, if f(partition_of(A))>f(partition_of(B), thread A is more likely to run than thread B. The function f(X) is constructed for each thread to be compared until the thread with the highest f(X) is determined. The thread with the highest f(X) may be determined to be the “thread most likely to run next” and its associated adaptive partition may be billed accordingly for the running time of the thread holding the mutex once the adaptive partition associated with the thread holding the mutex has exhausted its guranteed CPU budget.
• The systems and methods described above may be configured to run in a transaction processing system where it is more important to continue to process some fraction of the offered load rather than to fail completely in the event of an overload of processing capacity of the system. Examples of such applications include Internet routers and telephone switches. The systems and methods also may be configured to run in other real-time operating system environments, such as automotive and aerospace environments, where critical processes may be designated that need to be executed during critical events. An example may be in an automotive environment, where an airbag deployment event is a low probability event, but must be allocated processor budget should the event be initiated.
• The systems and methods also may be configured to operate in an environment where untrusted applications may be in use. In such situations, applications such as Java applets may be downloaded to execute in the operating system, but the nature of the application may allow the untrusted application to take over the system and create an infinite loop. The operating system designer will not want such a situation, and may create appropriate adaptive partitions so the untrusted application may be run in isolation, while limiting access to CPU time which other processes will have need of.
• While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.

Claims (29)

1. A system comprising:

a processor;

one or more memory storage units;

software code stored in the one or more memory storage units,

where the software code is executable by the processor to generate a plurality of adaptive partitions that are each associated with one or more process threads, where each of the plurality of adaptive partitions has a corresponding processor time budget, and where a critical adaptive partition of the plurality of adaptive partitions is associated with at least one critical thread and has a corresponding critical time budget, and

where the software code further comprises a scheduling system executable by the processor for selectively allocating the processor to the process threads based, at least in part, on the processor time budgets of the respective adaptive partitions, where the scheduling system may allocate the processor to the critical thread based on an available amount of the critical time budget of the critical adaptive partition even when the processor time budget of the critical adaptive partition has been exhausted.

2. The system ofclaim 1, where the scheduling system only bills the critical time budget of the critical adaptive partition when the processor is overloaded and the critical time budget for the critical adaptive partition is concurrently exhausted.

3. The system ofclaim 1, where the at least one critical thread is initiated by a processor interrupt.

4. The system ofclaim 1, where the at least one critical thread is a child thread of a critical parent thread.

5. The system ofclaim 1, where the at least one critical thread is designated as non-critical when it enters a blocking state.

6. The system ofclaim 1, where the at least one critical thread is designated as critical by an API.

7. The system ofclaim 1, where the scheduling system is a part of an operating system.

8. The system ofclaim 1, where the processor is a symmetric multiprocessor.

9. The system ofclaim 1, where the scheduling system microbills the processor time budget of an adaptive partition associated with a given thread for processor allocation used by the given thread.

10. The system ofclaim 1, where the scheduling system microbills the critical processor budget of the critical adaptive partition for processor allocation used by the critical thread.

11. The system ofclaim 1, where the processor time budget comprises a guaranteed portion of an entire time budget available for running the process threads on the processor.

12. A method of operating a process scheduler in a processing system having a processor and a plurality of software threads executable by the processor, the method comprising:

associating a first set of software threads with a first adaptive partition;

assigning a first processor time budget to the first adaptive partition;

associating a second set of software threads with a second adaptive partition;

assigning a second processor time budget to the second adaptive partition;

assigning a critical state to one or more software threads of the first or second set of software threads;

assigning a critical time budget to each adaptive partition associated with a critical thread;

selectively allocating the processor to run software threads of the first and second set of software threads based, at least in part, on the processor time budgets of the first and second adaptive partitions, respectively; and

selectively allocating the processor to run a critical thread based on an available amount of the critical time budget of the adaptive partition associated with the critical thread even though the processor time budget of the associated adaptive partition is exhausted.

13. The method ofclaim 12, and further comprising:

billing the critical time budget of the associated adaptive partition for processor allocation used by the critical thread when the processor time budget of the associated adaptive partition is exhausted and the processor is concurrently overloaded.

14. The method ofclaim 12, and further comprising:

microbilling the critical time budget of the associated adaptive partition for processor allocation used by the critical thread when the processor time budget of the associated adaptive partition is exhausted and the processor is concurrently overloaded.

15. The method ofclaim 12, and further comprising:

generating an interrupt thread in response to a processor interrupt; and

assigning a critical state to the interrupt thread.

16. The method ofclaim 12, and further comprising:

generating a child thread from a critical parent thread; and

assigning a critical state to the child thread.

17. The method ofclaim 12, and further comprising:

designating a critical thread as non-critical when the critical thread enters a blocking state.

18. The method ofclaim 12, and further comprising:

using an API to assign a critical state to one or more of the software threads.

19. The method ofclaim 12, and further comprising:

microbilling the processor time budget of an adaptive partition associated with a given software thread for processor allocation used by the given software thread.

20. One or more memory storage units comprising:

software code executable by a processor to generate a plurality of adaptive partitions that are each associated with one or more process threads, where each of the plurality of adaptive partitions has a corresponding processor time budget, and where a critical adaptive partition of the plurality of adaptive partitions is associated with at least one critical thread and has a corresponding critical time budget, and

a scheduling system executable by the processor for selectively allocating the processor to run the process threads based, at least in part, on the processor time budgets of the respective adaptive partitions, where the scheduling system may allocate the processor to run the critical thread based on an available amount of the critical time budget of the critical adaptive partition even when the processor time budget of the critical adaptive partition is exhausted.

21. The one or more memory storage units ofclaim 20, where the scheduling system only bills the critical time budget of the critical adaptive partition when the processor is overloaded and the critical time budget for the critical adaptive partition is exhausted.

22. The one or more memory storage units ofclaim 20, where the at least one critical thread is initiated by a processor interrupt.

23. The one or more memory storage units ofclaim 20, where the at least one critical thread is a child thread of a critical parent thread.

24. The one or more memory storage units ofclaim 20, where the at least one critical thread is designated as non-critical when it enters a blocking state.

25. The one or more memory storage units ofclaim 20, where the at least one critical thread is designated as critical by an API.

26. The one or more storage units ofclaim 20, where the software code further comprises an operating system and where the operating system includes the scheduling system.

27. The one or more storage units ofclaim 20, where the software code is executable in a symmetric multiprocessor.

28. The one or more storage units ofclaim 20, where the scheduling system microbills the processor time budget of an adaptive partition associated with a given thread for processor allocation used to run the given thread.

29. The system ofclaim 21, where the scheduling system microbills the critical processor budget of the critical adaptive partition for processor allocation used to run the critical thread.

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